1. Field of the Invention
The present invention relates to an electronic apparatus that can be operated in a selected mode of a plurality of operating modes, and more particularly to an electronic apparatus such as an electronic desk-top calculator, word-processor or electronic typewriter having a display unit and a data input unit and which can be operated by selecting a desired operating mode.
2. Description of the Prior Art
As an example of this type of electronic apparatus an explanation will be made of an electronic desk-top calculator. The principal components of LSIs and a display unit in such an apparatus can be classified as follows.
In the first group, a PMOS type LSI is used and a fluorescent display tube is used as the display unit. PA1 In the second group, a CMOS LSI is used and a liquid crystal display is used as the display unit.
The combination in the first group has the disadvantage that both the LSIs and the display unit consume a large amount of electrical power, but has the advantage that the display is very easily read. On the other hand, the combination in the second group has the advantage that both the electrical power consumption by the LSIs and the display unit is very low, but has the disadvantage that the display is hard to read
Furthermore, in order to set various modes, an electronic desk-top calculator according to the combination in the first group has various mechanical switches in order to specify modes such as rounding to the nearest whole number, inserting a decimal point or printing so that the mode setting does not change even when the power supply is turned off. On the other hand, a low-priced calculator according to the combination in the second group has special mode display symbols in a portion of the display unit which is different from the data display portion, and mode setting is performed by specifying a desired symbol by a touch-key. Furthermore, the use of a CMOS LSI which has low power consumption means that the set mode is stored when operation is interrupted by pressing an OFF key, so that the mode setting once made does not change.
In recent years, advances in semiconductor technologies have led to the commercial availability of CMOS LSIs with high-voltage resistance specifications. As a result, a third combination is becoming possible in which CMOS LSIs are used together with a fluorescent display tube used in the display unit.
This third combination requires, however, the provision of special mode display symbols, leading to the disadvantages of a complicated arrangement in the display unit and accordingly a high cost.
Apart from the above-mentioned problems, in recent years the number of functions which can be executed by this type of electronic apparatus has increased dramatically. An electronic desk-top calculator, for instance, has a number of different operating modes relating to calculations and display, and a large number of keys are required so as to specify those modes.
In opposition to the increase in size of such keyboards, however, the advances in LSI have resulted in that the overall size of the main unit of such apparatuses has become compact.
This leads to the disadvantage that the number of keys to be pressed has increased dramatically, so that operability has been decreased.